GNSS (global navigation satellite system) receivers determine their position by making accurate range measurements to transmitting satellites. However, the accuracy may be severely decreased if the signals are distorted by multi-path effects. Typically a multi-path environment is especially bad in urban areas where there are many reflecting surfaces as shown in FIG. 1. Unfortunately, many mobile phone users live in the urban areas as well.
Traditionally GNSS receivers try to minimize the harmful effect of multi-path by making the range measurements less sensitive to multi-path. Several such methods are known, e.g., a narrow correlator described by A. J. van Dierendonck, P Fenton and T. Ford in “Theory and Performance of Narrow Correlator Spacing in a GPS Receiver”, Navigation, Vol. 39, No. 3, Fall 1992, pp. 265-283, a strobe correlator described by L. Garin, F. van Diggelen and J-M. Rousseau, in “Strobe & Edge Correlator Multi-path Mitigation for Code”, ION GPS-96, Sep. 17-20, 1996, Kansas City, Mo., pp. 657-664, and a multi-path estimating delay lock loop described by R. D. J. van Nee, in “The Multi-path Estimating Delay Lock Loop”, ISSSTA-92, Nov. 29-Dec. 2, 1992, Yokohama, Japan, pp. 39-42.
Typically a GPS (global positioning system) receiver sees 8-12 satellites simultaneously. In the future, when a European Galileo system is operational, the number of visible satellites will be doubled to 16-24 for a combined GPS-Galileo receiver. However, only four satellites are needed for a position calculation. Hence it would be advantageous to select for position calculation the signals that are the least corrupted by a multi-path propagation.